Ahhhhh!!!! Trying to cut thread with die

Hi all got to the last straw and threw bar through window. I can't take no more. I am trying to put an M8 thread on some bar stock with a die. Turned bar down to 8mm no good, 7.8mm still will not take, 7.5mm still will not start. What am I doing wrong. I always fail at this point. Even making a little oscillating engine I have stopped at putting a thread on the shaft m4 bought new die from rdg and still have same issue. The funny thing is the m8 thread is for a home made tail stock die holder. Ironic..... Regards mike

Have you tried chamfering the end of the rod to give the die a "start".

Mick

Also look at the die, like a taper tap they usually have one side with a lead-in which is most often on the side with the writing.

Use the central screw of your diestock to spread the die a little which will also help it to start, once you have cut the thread at this setting it can be tested against the tapped hole and the die closed up a bit if nedd

Assuming you have the rod in teh lathe and are using a standard diestock another trick is to bring teh tailstock barrel up to the back of teh diestock and apply a little pressure as you turn it by hand, this also helps keep the die square to the work

Edited By JasonB on 03/08/2013 08:08:56

Hi both thanks for the reply. I have chamfer on bar. Also putting tail stock up against die holder but still no joy. I have got to the stage that when applying pressure with the tail stock. I can put the lathe on jog and actually stop the lathe with the amount of pressure I had put on it. It must be cheap metric dies I have. They don't have a split in them.

There are some cheap dies on the market that are totally useless on any sort of steel. Colin

Just another thought....is the lathe in reverse? I've tried that before! Colin  Perhaps i'm not fully awake yet!   I just assumed for some unknown reason that you were trying to thread your bar under power as I often do,being in favour of using as little effort as I can get away with.     Colin 

Edited By colin hawes on 03/08/2013 08:43:36

Drill and tap the bar M8 then screw in some threaded bar or a set screw and cut off to length.

It doesn't resolve the die problem but at least you get a perfect thread right up to the shoulder.

Have you tried screwing a standard M6 bolt into the 'die' you have (just to check its not a left hand one! Dont laugh it does happen.

I recently reground a good quality, brand new 15mm drill that would not even open up a 12mm hole in aluminium. It had been sharpened as a left hand drill!

Totally unrelated but many years ago I spent hours hours trying to diagnose a fault on a precision AC millivoltmeter I was making and eventually found a IN4148 diode (a very common component) which had its marking band at the wrong end. During fault finding I had even disconnected components and checked with a meter that it was a working diode.

Ian P

Edit, I should have said M8

Also, I think it unlikely you will end up with a good/nice thread using a solid die, my understanding is that they are mostly used for cleaning up damaged threads.

I recently

Edited By Ian Phillips on 03/08/2013 09:04:46

A Dremel type grinder can cut a slit in a solid die and make it more useable. I've done it. Colin

8mm is pretty big for a cut from zero

The best way to do threading, especially the bigger diameters is to cut most of the thread on a lathe, then tidy it up with a die

The added advantage is you get a thread which is definitely at 90 degrees to the bar

Machines which thread 8, 10mm bar etc with a die usually weigh around a ton and have big chunky die cutting bits, like herbert turret lathes

Even if you got it to start cutting... there's a 50% chance it would be a wonky thread when you screwed on the nut

As Ian said try a bolt through the die. The die is made by tapping a hole in it then cutting the 3 clover petals round the edge which is supposed to form the cutting lip. This throws up a burr on the threaded edge which they don't clean on cheap items so you don't have a cutter at all. Look very closely at the cutting edge, think about cutting geometry, and grind out the edge with a Dremel.

Hi All,Thanks for the replies. The die kit was cheap it was purchased off ebay. I think i paid £10 for 10 taps and dies. I will have a go at splitting the die with my dremel. As I think this will give me more ground. I have an imperial lathe Boxford with screwcutting gearbox but if I put an imperial thread on the bar then I dont have an imperial tap to thread the hole in the project. (Tailstock Die holder) Its only to add a handle to the bar. Thanks again.Regards Mike

For all my metric threading I use a guided die stock that I made my self. Not only does it stop the thread from wobbling around like a satuday night drunk but it also allows you to push a little harder to get it to bite. I would get a hss die though. I have seen good offerings for around £30.00. I'm sure if you ask on here you will get some good pointers as to where to get one from. If you just wanted an m8 die then arc euro trade do one for £5.40.

David

Mike: Don't waste more time, put the cheap set of taps and dies in the bin. Buy a decent brand split die and I expect your problem will disappear. Thirty odd years ago I bought a 'cheap' set of metric taps and dies. After one trial cut I threw them away and now only buy branded taps and dies.

There are two rules for buying cutting tools:

1. Never buy cheap cutting tools, they're a total waste of money

2. See rule 1

Regards,

Andrew

Michael, I had the same problem and got good advice on the forum here (search for Dies etc.). You can cut the bar undersize by up to 10% and still get an acceptable thread as there is a certain amount of an extrusion effect as you cut with the die. Taper the end as suggested. I must agree that most of the cheap dies are a total waste of money. You must look at the dies under a magnifying glass to see how badly cut /shaped they actually are. Most have the three holes punched through at manufacture and the cutting edge is mis-shapen and rounded and just couldn't cut. You can try to improve them by dressing the hole with a round chainsaw file but really if you are going to be doing much threading there is no substitute for a properly made die. They are not cheap at anything from about £6 upwards each. Just buy what you need and you will be amazed at the difference.

Michael

I agree - don't buy cheap tools - they usually equate with poor quality. As far as threading tools go just buy the sizes you need at the very best quality you can afford. If you buy sets you will find, years down the line, that there are some sizes you have never used. When starting a new construction project just go through the drawings and see the sizes you will need - then buy those you don't have already.

Regards

Norman

As the die is solid, and ex-ebay, are you sure it is a threading die (cutter), and not just a thread chaser (used to trim up existing threads).

Re tools in general, I had to extend the thread on some existing 9/16" BSF bolts. These just laughed at a cheaper die, but lay down and surrendered when I got an HSS one from Tracy Tools.

Phil

The non split dies seem to be quite common, but they are just die nut without the hexigon. There was an artical in ME a few years back about one of the supply firms, they had a grinder set up to slit the dies, think they got their supply of dies from a country in continental Europe. Ian S C

Cheap dies and taps are good for cleaning up existing threads, don't throw them away, don't ever throw anything away. Solid dies can be split with a narrow cutting disc and a chamfer put on the cut, but still not usually much good. I.ve found that a big reduction in diameter usually works, I see 10 % suggested.

Thanks all, very good advice. I have been reading this forum for over a year and subscribe to mew but never posted here. Thanks again, will just purchase what I need. Regards mike